For over twenty-five years, vanadium has been considered for use in flow batteries. In this design, two electrolyte solutions, each containing vanadium ions, are pumped through a cell where some of the ions are reduced and others are oxidized to produce an electrical potential. By reversing this process the battery is recharged.
The concept of a flow battery containing vanadium is of interest because of the chemical properties of vanadium. A number of problems, however, have held back the commercialization of this technology. While vanadium salts are soluble in water, their limited concentrations restrict the energy density of the battery. Furthermore, a cumbersome arrangement of holding tanks and pumps add to the bulk of the system, reducing its appeal.